How running pace is calculated
Pace is finish time divided by distance. Run 10 km in 50 minutes and your pace is 50 divided by 10, or 5:00 per km. That is the whole formula. The fiddly part is the unit math, because distance and time mix decimal numbers (kilometers) with base-60 numbers (minutes and seconds), and most people do the arithmetic in their head while tired.
This calculator keeps pace internally as seconds per kilometer and converts at the display layer, so the three modes stay consistent. Enter any two of distance, time, and pace, and it returns the third. Mode Pace takes distance and time. Mode Time takes distance and pace. Mode Distance takes pace and time.
time = pace × distance
distance = time / pace
min/km versus min/mile
A mile is 1.609344 km, so a per-mile pace is always a larger number than the same effort expressed per km. To convert, multiply your per-km pace by 1.609344. A 5:00/km pace works out to about 8:03/mile. Going the other way, divide per-mile pace by 1.609344.
The unit toggle handles this for you. Flip it and the distance input, the pace input, the splits, and the speed readout all switch together. Internally nothing changes; only the display converts. That matters because mixing units (a km distance next to a per-mile pace) is the easiest way to set a wrong race goal.
One quirk worth knowing: pace and speed are reciprocals. A 6:00/km pace is 10 km/h. A 4:00/km pace is 15 km/h. If you train on a treadmill that only shows speed, the summary card gives you km/h and mph next to the pace so you can match the dial.
Even splits versus negative splits
The split table assumes even pacing: every kilometer (or mile) takes the same time. It is a clean planning view, and it is what you would run in a perfect world. Most strong races are run slightly differently.
A negative split means running the second half faster than the first. For the marathon especially, starting 2 to 4 percent slower than goal pace and speeding up late is the pacing pattern most associated with personal bests, because it protects against the glycogen depletion and fade that wrecks the final 10 km. A positive split (going out too fast and slowing) is the most common way amateurs blow up.
Use the even-split table as your average target, then plan to bank nothing early. If the table says 5:41/km for a sub-4 marathon, run the first few km at 5:43 to 5:45 and let the pace come down as you warm up. The math gives you the average; race craft is how you distribute it.
Common race paces for reference
These are the average paces needed to hit round finish times. Handy for sanity-checking a goal before you commit to it.
- 5 km in 30:00 = 6:00/km (9:39/mile)
- 5 km in 25:00 = 5:00/km (8:03/mile)
- 5 km in 20:00 = 4:00/km (6:26/mile)
- 10 km in 50:00 = 5:00/km (8:03/mile)
- Half marathon in 2:00:00 = 5:41/km (9:09/mile)
- Half marathon in 1:45:00 = 4:58/km (8:01/mile)
- Marathon in 4:00:00 = 5:41/km (9:09/mile)
- Marathon in 3:30:00 = 4:58/km (8:01/mile)
- Marathon in 3:00:00 = 4:16/km (6:52/mile)
Turning a pace into a plan
A target pace only means something if your training supports it. If you want to know what pace your current fitness predicts, run our VDOT calculator to get training and race paces from a recent race result. To see your projected times across every distance, the race time predictor takes one result and fills in the rest. And if you are working backward from a race date, the guide on how long marathon training takes covers how many weeks the goal pace actually needs.
Frequently asked
Does the calculator work in miles?
Yes. The Miles toggle switches the distance input, the pace input, the split table, and the speed readout to imperial units at once. Pick the unit before you type so the inputs read in the system you are thinking in.
How do I enter a custom distance?
Choose "Custom…" in the distance dropdown and a number field appears. The unit of that field follows the toggle, so it asks for km when you are in metric and miles when you are in imperial.
Why does the split table stop at a certain number of rows?
For long distances the table would run to dozens of rows, so it caps and shows the splits up to a sensible limit while the summary card still reports the full finish time. The cumulative column on the last visible row tells you where you stand at that mark.
What is the difference between pace and speed?
Pace is minutes per distance and speed is distance per hour. They are reciprocals of each other. A 6:00/km pace is the same as 10 km/h. The summary card shows both so you can read whichever your watch or treadmill uses.